The present invention relates to nuclear reactor fuel bundles such as are used in reactors of the pressurized water or boiling water type. In such bundles, fissionable fuel is disposed within elongated tubular fuel rods which are mounted in parallel array between a pair of end plates. When the bundle is in service in a nuclear power reactor, water passes along the outer surface of the fuel rods, receiving heat therefrom owing to the reaction occurring inside. In order to permit uniform heat removal and to avoid overheating of the rods, it is necessary that they be accurately spaced apart laterally. Maintaining the spacing of the elongated rods in such a closely spaced array under conditions in which vibration naturally occurs, requires a carefully designed spacer unit which has been the subject of many prior art patents. In particular, the present invention may be used with a spacer of the type described in U.S. Pat. No. 3,852,154 assigned to the assignee of the present invention, which is incorporated by reference into the present application.
In the spacer design of the referenced patent, a corner mounted spring engages the side of fuel rods passing through each of the grid openings formed by the spacer and holds the fuel rod against protrusions which have been formed from the grid walls. This three-point engagement provides a stable positioning of the fuel rod within the spacer. In a typical fuel bundle there are a plurality of spacers disposed along the length of the fuel rod. In order to assure proper positioning during operation, the spacers must be secured in the desired position; otherwise, they may be displaced along the longitudinal direction of the fuel rods due to the vibration and the flow of water adjacent the tubes. Typical prior art devices which perform the function of securing a grid spacer against movement, may be found in British Pat. No. 1,148,881, U.S. Pat. No. 3,802,995, and U. S. application Ser. No. 385,312, now U.S. Pat. No. 3,984,284, assigned to the same assignee as the present invention. None of these prior art devices are considered to include the elements of the present invention. The present invention provides a simple and improved construction to secure the grid spacer in the desired position and which avoids the problems typical of prior art arrangements for securement of these spacers.